Patent document 1, for example, discloses a sensor that detects an amount of particulate matter (hereinafter referred to also as “PM”) contained in an exhaust gas of an internal combustion engine. The sensor disclosed in patent document 1 includes an insulating layer on which the PM is deposited and a pair of electrodes spaced apart from each other at the insulating layer. When the exhaust gas contacts with the sensor, PM in the exhaust gas is deposited between the electrodes. Conductivity across the electrodes varies in accordance with the amount of PM deposited, and resistance across the electrodes varies. Thus, the amount of PM deposited between the electrodes can be detected by detecting the resistance across electrodes of the sensor, and the amount of PM contained in the exhaust gas can be accordingly estimated to detect a fault in a PM trapping filter, etc.
If the amount of PM deposited between the electrodes exceeds a predetermined level in this sensor, a value of the resistance across the electrodes no longer changes. The sensor then cannot output a value corresponding to the amount of PM deposited. In such situation where a lot of PM deposit between the electrodes, in the technique disclosed in patent document 1, a PM reset that burns the deposited PM to remove them is performed by heating the sensor for a predetermined period of time with a heater embedded in the sensor.